Despite the prevalence of isocyanate-induced respiratory diseases, medical experts still have a poor understooding of how the chemicals cause allergic and asthmatic diseases. Typically, exposure to a foreign body such as a chemical like an isocyanate results in the production of antibodies that specifically recognize the foreign body. Antibodies differ slightly in their chemical structure, function, and location in the body. IgG, the most common subclass, circulate in the blood stream. IgE antibodies reside primarily in the respiratory tract, including the nasal cavity and lung, attacking inhaled invaders. Overproduction of IgE antibodies specificity directed against an allergen often results in an allergic reaction when the person breathes in air contaminated with that allergen.

A puzzling aspect of TDI exposure is that no TDI specific IgE type antibodies are found in people with TDI induced airway diseases. Instead, TDI-exposed individuals have significantly higher total IgE levels that lack TDI specificity. However, they do have TDI-specific IgG type antibodies circulating in the blood, but these are not thought to participate in the allergic responsesThe bottom line is this: TDI exposure results in specific antibodies of one class -- IgG in the blood -- but not another -- IgE in the lungs and nose. And yet, most, if not all, of the health problems are occurring in the respiratory tract.